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NUMBER   OF   SPECIES

oceanic in origin. The continents and oceans are peopled by
rather over three thousand species of Mammalia, a number which
is considerably loss than that of either birds or reptiles. It
seems clear that, so far at any rate as concerns the numberK of
families and genera, the mammalian fauna, of to-day in less varied
than it was during the Mid - tertiary period, the heyday of
mammalian life. It is rather remarkable to contrast in this way
the mammals and the birds. The two <jliusst»s of the animal
kingdom seem to have come into being at about the name period ;
but the birds either have reached their culminating point to-day,
or have not yet readied it. The Mammalia, on the oilier hand,
multiplied to an extraordinary extent during the Kotvno and tho
Miocene periods, and have nince dwindled. The break in most
marked at the close of tho Pleistocene, and may be in part due
to the direct influence of man. At present man ex^reinen «>
enormous an affect, both directly and indirectly, that the future
history of the Mammalia is probably foreshadowed by the, in-
stances of the White Rhinoceros and the Quugga, On the other
hand, the economic usefulness of the Mammalia is greater than
that of any other animals; and the next moat important era
in their history will be probably that of domesticity and " pre-
servation/*